This study is designed to complete the longitudinal investigation of cognitive event-related potentials (ERPs) in a cohort of outpatient schizophrenics and their siblings. The focus is on the somatosensory late positive component (P300), as well as early ERP events. The study groups include: (1) 40 outpatient RDC schizophrenics repeat tested four times at approximately six month intervals; (2) 40 "never mentally ill" siblings repeated two times at approximately 12 month intervals; (3) 40 "schizophrenia spectrum disorder" siblings; (4) 40 nonpatient controls. All schizophrenics will meet both DSM-III-R and SADS-L criteria for schizophrenia (chronic subtype), and may or may not have an Axis II personality disorder. The findings from this study should help to determine the extent to which cognitive ERP deviations, in a cohort of schizophrenic patients, are the reflection of psychotic decompensation or a basic neurophysiological defect that persists across clinical states. In addition, it will be possible to assess the extent to which these abnormalities trail into siblings of schizophrenic probands. Two follow-up studies are proposed. With a modified somatosensory paradigm using four fingers, we will evaluate the P300/Nd difference wave relationship as well as the "cognitive P40 phenomenon" in a cohort of 20 RDC schizophrenics and 20 matched nonpatient controls. Although this "early cognitive effect" has been obtained primarily in healthy control subjects, there is new evidence that this effect may also be experimentally manipulated in schizophrenic patients. Findings from this proposal should help to determine the earliest sign of measurable attentional dysfunction in schizophrenia. The next study will combine an ERP/reaction time paradigm using the Sternberg memory-scanning task to examine P300 components in 20 schizophrenics and 20 nonpatient controls within a different mode of cognitive operation. This will help determine whether P300 amplitude reduction in schizophrenia reflects a CNS alteration limited to attentional processing or whether the same alteration is manifested during other modes of cognitive operation.